From Bulbapedia, the community-driven Pokémon encyclopedia.
Acid rain is a glitch in Pokémon Platinum that results in the simultaneous occurrence of all weather conditions at once, thus damaging all Pokémon on the field. Even though it was found out before the english release of the game, it is in both the japanese and english versions.
While it is either hailing or there is a sandstorm, if a player of Platinum uses Pursuit on a Pokémon that is switching out on that turn and causes it to faint, the glitch will activate. Upon sending out the next Pokémon, the weather will have changed, and all four weather conditions will be going on at once until the end of the battle.
This will occur if the user of Pursuit is the host, even if the host is Diamond or Pearl.
If Trickroom, gravity, or uproar is in effect when the glitch is activated, they will activate the glitch, along with any other effects with priority bellow it. The priority is: Trick room --> Gravity --> Uproar --> Fog(hurts after animation) --> Hail(hurts after animation) ---> Sunshine(hurts after animation) ---> Sandstorm(hurts after animation) ---> Rain(Hurts after animation. Glitch cannot be activated using this weather)
Other moves with multiple-turn effects such as Mud Sport, Water Sport, Tailwind, and Perish Song will not be affected and work as normal.
Even if the Pokémon is normally immune to a weather condition due to its type (Template:Type2s with hail and Rock-, Ground-, and Template:Type2s with a sandstorm), they will accumulate damage four times each turn, with the cause of the damage identified as their ability, rather than the weather. In this way, a Pikachu in battle can be hurt by its Static, or a Buizel by its Swift Swim.
Conversely, a Pokémon with an ability that heals it in certain weather conditions, such as Ice Body or Rain Dish, will not take damage, but instead be healed four times a turn untill they are fully healed, then the weather will hurt it. An ability that heals in some weather and hurts in other weather will work as it normally does, healing with one condition and hurting with the other.
Both Thunder and Blizzard have 100% accuracy, due to simultaneous rain and hail, while SolarBeam requires no charging due to the sun.
If a Castform or Cherrim is brought into battle, their ability will cause them to constantly transform, thus locking up the battle until the game is turned off. Castform, strangely, will only transform between its Sun and Rain forms.
*Indicates glitches which have been officially acknowledged